1. Field of the Invention
The present invention relates to an optical module comprising an optical fiber and a light-emitting element and/or light-receiving element used in an optical data transmission device, and a method for manufacturing same.
2. Description of Related Art
FIG. 6 and FIG. 7 give general views of one example of a conventional optical module comprising optical fibers, a light-emitting element and/or a light-receiving element. FIG. 6 is an oblique view of an optical module and FIG. 7 shows the structure of a section cut along plane B in FIG. 6.
An `optical module` is a general term for an optical transmission module comprising an optical fiber and a light-emitting element, an optical reception module comprising an optical fiber and a light-receiving element, or an optical transmission and reception module comprising an optical fiber, light-emitting element and light-receiving element.
According to FIG. 6 and FIG. 7, the optical module 100 comprises an Si substrate 102, an optical semiconductor element 104 and an optical fiber 106. An LD chip forming the optical semiconductor element 104 is provided in a respective position on the upper face of the Si substrate 102.
A V-shaped groove 102x is formed on top of the Si substrate 102, and an optical fiber 106 is mounted in this V-shaped groove 102x in such a manner that it contacts both walls thereof. A fiber cover 108 is provided in such a fashion that it covers the optical fiber 106. The fiber cover 108 and Si substrate 102 are bonded by means of an ultraviolet-setting adhesive. Thereby, the optical fiber 106 is secured under pressure between the fiber cover 108 and the Si substrate 102. Moreover, an anode electrode 110 and a cathode electrode 112 are respectively provided in an electrically unconnected fashion on the upper face of the Si substrate 102, at distant positions from the light input face 106a of the optical fiber 106. These electrodes 110 and 112 are laminated films formed by successively layering Ti film, Pt film and Au film onto the Si substrate 102. Moreover, an LD chip 104 is fixed by Au/Sn soldering onto the anode electrode 110. A light output face 104a of the LD chip 104 opposes the light input face 106a of the optical fiber 106. The LD chip 104 and optical fiber 106 are respectively positioned with very high accuracy by means of a dicing half-cut 101 formed in the Si substrate 102, in such a manner that light output by the LD chip enters into the optical fiber 106. Moreover, the upper face of the LD chip 104 and the cathode electrode 112 are connected by means of wire bonding 114.
Furthermore, this optical module is sealed by means of a resin, in such a manner that the whole of the LD chip 104 and the portion of the optical fiber 106 on the light input face 106a side thereof are covered, as illustrated in FIG. 7. In FIG. 6, this resin is omitted from the drawing in order to describe the internal composition of the module 100. Hereinafter, the sealed portion of the module is called the sealing section 116. Moreover, the resin in the sealing section 116 is called `potting resin`, for which an Si resin, which is a thermosetting resin, is used.
The manufacture of an optical module 100 of this kind is performed as described below, for example. Firstly, a V-shaped groove 102x is formed by an etching process in the region of the Si substrate 102 where an optical fiber is to be installed. Thereupon, a Ti film, Pt film and Au film are layered in that order onto the upper face of the Si substrate 102, by means of sputtering. Consequently, a laminated film (Ti--Pt--Au film) is formed on the upper face of the Si substrate 102. Thereupon, the laminated film is patterned by means of photolithography and subsequent etching processes, in such a manner that it forms a cathode electrode-shaped and anode electrode-shaped pattern. Next, an optical axis direction positioning groove (called a `dicing half cut`) 101 for an LD chip and optical fiber is formed in the Si substrate 102. Thereupon, an LD chip 104 is located in position over the anode electrode-shaped pattern by a marker alignment process, whereupon it is fixed by means of Au/Sn solder. The upper face of the LD chip 104 and the cathode electrode-shaped pattern are connected by means of wire bonding 114. Thereby, the anode electrode-shaped pattern forms an anode electrode 110, and the cathode electrode-shaped pattern forms a cathode electrode 112. Next, the optical fiber 106 is mounted in the V-shaped groove 102x , whilst positioning same in the optical axis direction with respect to the LD chip by means of the dicing half-cut 101 provided in the substrate 102. Thereupon, a fiber cover 108 is provided in such a manner that it covers the optical fiber 106, and the fiber cover 108 and Si substrate 102 are bonded together by means of an ultraviolet-setting adhesive.
Next, an Si resin forming the potting resin is applied on in such a manner that it covers the whole of the LD chip 104 and the portion of the optical fiber 106 on the light input side 106a thereof. Next, the resin is hardened by heating the assembly in an oven at a temperature of 130-150.degree. C. Thereby, a sealing section 116 is formed.
However, in the process of forming the aforementioned sealing section 116, during the hardening of the potting resin by means of the heating process, loosening of the resin may occur, due to physical causes such as decline in the viscosity of the resin below the viscosity immediately after the application thereof, or decline in the surface tension of the resin. Therefore, after heat treatment, the potting resin does not provide a satisfactory cover over the LD chip 104 and the optical coupling section 118 between the LD chip 104 and the optical fiber 106 (indicating the region between the light output face 104a of the LD 104 and the light input face 106a of the optical fiber 106). When the optical coupling section 118 is exposed to the external atmosphere, the constituent components of the elements are oxidized by oxygen in the air, for example, and there is a risk that this may cause degradation of device reliability. Moreover, in order to prevent this degradation of device reliability, in other words, in order to obtain a sealing section 116 of sufficient thickness, the potting resin coating process and heating processing must be repeated a number of times in order to form a sealing section 116 (116a, 116b, 116c) comprising a plurality of layers (FIG. 7).